The invention concerns a bristle for brushware or brushes, which is produced by cutting an extruded monofilament to length, and which tapers towards its useful end in a point-like manner, which is made from at least two co-extruded plastic components and has a shaft made from a soft elastic plastic and a core made from a flexible plastic which is harder than that of the shaft, wherein the core projects past the jacket at the use sided end to form a pointed tip. The invention also concerns a method for the manufacture of such bristles and a brush having such bristles.
The effectivity of a tooth brush for cleaning teeth and for tooth care depends mainly on the structure and function of the bristles in addition to the duration of the cleaning time. In the development of tooth brushes, the bristle material, bristle geometry, and the combination of the bristles within the bristle stock are therefore very important. The bristle stock or the bristles forming same must fulfil several functions in tooth care. They must reach the spherical lateral surfaces on the inner and outer sides of the teeth having largely varying curvatures and the useful end of the bristle and/or bristle jacket must work sufficiently effectively. Moreover, at least individual bristles of the bristle stock should penetrate into the interdental spaces from the inner and outer side of the teeth and the bristles should also exert a massaging action on the gum and, in particular, on the gum edges. Cleaning of the teeth and of the interdental spaces should, in conjunction with the dentifrice used, not only prevent plaque build-up but also remove existing plaque to prevent caries.
Dental tests have shown that in countries where caries prophylaxis is practiced, caries is rarely found on free and substantially flat tooth surfaces because these surfaces are easy to reach and clean with conventional dental hygiene means, such as tooth cleaning means, i.e. tooth brushes, dental floss etc. Moreover, prophylactic dentifrices which contain e.g. fluorides, can easily reach and treat these surfaces.
Recent studies have shown that approximately 80% of caries originates in the so-called dental fissures most of which are located on the chewing surfaces of the molars and premolars, which are therefore more prone to caries and to larger cavities. These gap-like fissures of very narrow cross-sections are, in and of themselves, an ecosystem which are difficult or impossible to reach with conventional tooth brushes and which foster undisturbed development of caries-generating plaque. Nor do dentifrices reach these locations to a sufficient degree. Additionally, the enamel at the bottom of the fissures is very thin and contains few minerals which even enhances caries formation at these locations.
Modern dental medicine classifies such fissures according to their geometrical shape into U- V- and I-shaped fissures. These represent approximately 93% of the fissures examined. So-called ampoule-shaped fissures have a considerably reduced occurrence of approximately 7%. These fissures narrow like a funnel to a narrowest location and then widen again like a sack. Additionally, all fissures are curved in their longitudinal extension and the funnel axis is often tilted or curved. Cleaning of these fissures would require extremely thin bristles which would deflect under the smallest loads due to their insufficient bending strength. Fine thin bristles or bristles having finely drawn ends are also desired in other fields, e.g. cosmetic brushes or brushware.
DE 90 12 603 U proposes conification of the bristle ends and at least partially providing the bristle stock of a tooth brush with such bristles to be able to also reach, in particular, the interdental spaces and highly rugged surface structures. The same purpose is fulfilled by a two component bristle (GB 2 325 401 A) having the pre-characterizing features of claim 1. It is made from a shaft of soft elastic plastic e.g. nylon and a core which is harder than the shaft e.g. polyester, so that the conically tapered tip is substantially formed by the harder core. Another two component bristle (WO97/25 902A) has a core made from a plurality of monofilaments projecting past a closed jacket.
No concically tapered tip is envisioned nor would one be possible.
In a known tooth brush having a similar bristle design (EP 0 596 633), the main task is to achieve an improved flexibility in the region of the bristle ends with densely packed bristles and corresponding stability of the bundle, in order to, in particular, guarantee cleaning in the region of the gingival border without injuring the gingiva. Moreover, bristles are known (WO99/24649) which are separated at their ends into flags thereby mainly producing intensification of the bristle action due to multiplication of the bristle ends and action of the individual bristles over a larger surface region due to the flags.
Bristle tips have also been conventionally shaped by inserting them into a solventxe2x80x94as in dip varnishingxe2x80x94and slowly removing them thereby dissolving the plastic material of the bristle. The bristle end remains in the solvent bath for the longest period of time to thereby form bristles with pointed ends. The method is expensive, environmentally harmful, and the formation of the tip cannot be exactly controlled such that each bristle has a different geometrical shape at the end and therefore a different bending and wear behavior.
Pulsed extrusion of monofilaments is also known to obtain a monofilament with varying diameter. The monofilament is cut in the region of the constriction to obtain bristles having tapered ends. Pulsed extrusion cannot be carried out at the large frequencies which would be required for the short bristle lengths of many applications, thereby producing a substantial amount of waste. Moreover, the ends would have irregular shapes.
It is therefore the underlying purpose of the invention to introduce a bristle with tapering bristle end corresponding to GB 2 325 401A which has sufficient bending strength and simultaneously good action of the bristle end. The bristle should furthermore be designed such that it can be produced with reproducible properties.
A bristle of this type is characterized in accordance with the invention in that the soft elastic shaft is additionally surrounded by a jacket made from a plastic which stiffens the shaft.
The inventive bristle has a distinct tapering which permits penetration of the end into narrow gaps, e.g. into the fissures of teeth down to the fissure bottom and permits action on the fissure wall and fissure bottom by elastic deflection. The bristle core thereby provides sufficient bending strength and at the same time good elasticity. The soft, preferably rubber-elastic shaft has similar effects as an eraser due to its higher coefficient of friction. It achieves a more uniform cleaning action since the soft material adjusts well to uneven surfaces.
The degree and length of the tapering are matched such that the bristle end does not deflect, and thereby become ineffective, under small loads. The tapering bristle end is guided by the bristle shaft such that it can penetrate into narrow gaps, e.g. fissures, without premature bending of the bristle itself. The inventive bristle permits very precise application of media, e.g. cosmetics, lip gloss, eye liner etc.
The plastic materials of the core and of the shaft can be mainly selected with regard to their intended function, whereas the bristle jacket provides the required bending strength. When the bristle is bent, the jacket can effect additional cleaning or polishing.
As mentioned above, the shaft is preferably made from a rubber-elastic plastic material, in particular from an elastomer.
In a further preferred embodiment, the shaft and/or jacket extend conically towards the tip of the core, wherein the conical angle defines the bending behavior of the bristle end.
In a further advantageous embodiment, the core also tapers conically such that the conical length defines its bending behavior.
In another variant or in addition to the conical shape, the core can be disposed in the shaft in an axially displaceable fashion to adjust that free length of the core which projects past the shaft to the respective application.
To achieve the same object, the shaft and the jacket may be axially displaceable relative to one another to realize a stepped bristle comprising several components. In both above-mentioned embodiments comprising jacket, shaft and core, their different properties, substantially determined by their materials and geometry, can be effective in the region of the bristle end.
The core can have a round tip to prevent excessive action for short free lengths.
In a preferred embodiment, the core and the jacket are made from a thermoplastic material, whereas the shaft is preferably formed from a thermoplastic elastomer. Suitable thermoplastic materials are polyamides, polyester and also polyethylene or polypropylene.
The above-mentioned plastic materials can be fashioned by extrusion or coextrusion into endless monofilaments from which the bristles are then cut to the desired length.
The conical shape or the length of the conical end can be adjusted to the purpose of use andxe2x80x94for reasons of stabilityxe2x80x94to the cross-section of the bristle.
The tapering can have a maximum length of 2 mm, preferably between 0.1 and 1.00 mm, wherein the smallest diameter in the region of the outermost end should be between 0.01 and 0.03 mm. At a separation of 0.6 mm to approximately 1 mm from the bristle tip, the bristle diameter can expand progressively to the conventional size.
In a further advantageous fashion, at least the core is split once or several times in the region of its free end such that the bristle end elastically bends and spreads along the gaps when loaded. This produces an additional action on the walls of ampoule-shaped widenings, in particular of ampoule-shaped fissures which is also supported by the frictional effect of the shaft. Monofilament bristles of similar type which permit a directed spreading are described e.g. in WO 99/24649. In contrast thereto, the inventive bristle is characterized by even thinner xe2x80x9cflagsxe2x80x9d which are evenly packaged through integration into the shaft. The core is substantially produced according to methods described in WO 99/24649.
In accordance with another embodiment, at least the core of the bristle is split once or several times at a separation from its end such that when the bristle end is loaded, only the split region bulges under compression, thereby maintaining its closed end. This, too is a resilient process with corresponding restoring force. The bulge widens the cross-section and the curved bristle sections and edges act on the gaps, in particular of ampoule-shaped fissures.
In a further embodiment, the core can consist of two or more monofilaments whose free ends function as fibers.
In a further embodiment of the invention, the cross-section of the bristle has a material structure which changes from the inside to the outside. It can be realized by coextrusion of different materials or by defined embedding of fillers, e.g. color pigments, in the outer region.
It is thereby recommended to provide the material structure of the core with high elasticity and abrasive resistance and the jacket with a high bending strength. The inventive bristle is preferably produced by coextrusion of core and shaft, and optionally also the jacket, as a multiple component filament. Alternatively, the jacket can be extruded onto a coextruded shaft and core structure.
In a further embodiment, the bristle comprises abrasive means which are embedded at least in the region of the soft shaft to further support the xe2x80x9cabrasivexe2x80x9d cleaning effect.
Moreover, at least the shaft and the core may have different colors for visualization of their respective effects and to thereby simultaneously provide a kind of wear display, since the tapering core will generally be worn before the soft shaft such that the color of the core will gradually disappear.
The invention also concerns a method for producing bristles having the above-described structure. The multiple component monofilaments obtained by extrusion, larger strand sections of such monofilaments, or bristles cut to length are clamped at a separation from the free end, supported with the core on a circulating grinding surface, and conified through grinding at an inclination with respect to that grinding surface of approximately the cone angle. The applicant describes a technique suitable therefor in EP 0 444 436 A1.
In addition, the bristle can also be supported on the grinding surface at the jacket. This support permits exact conification of the soft rubber-elastic shaft which would otherwise be difficult to grind, and can be very precisely defined by corresponding setting of the cone angle.
Instead or additionally, the core and the shaft can be axially displaced relative to one another until a partial length of the core projects past the shaft. In the same fashion, the jacket and the shaft can be axially displaced relative to one another until a cylindrical partial length of the shaft projects past the jacket.
If the bristle is not conified before axial displacement, it assumes a stepped profile which tapers towards the free end. If conification takes place before, the components forming the bristles merge via inclined surfaces.
The method described by the applicant in EP 0 346 646 A1 is particularly advantageous for such bristle xe2x80x9ctopographyxe2x80x9d.
The invention also concerns a brush, in particular a tooth brush, comprising a bristle support and a bristle stock mounted thereto having individual bristles or bristles combined into bundles or groups. Such a brush is characterized in that the bristle stock comprises, at least partially, the above-described inventive bristles. These bristles may be optionally disposed only in defined regions of the bristle stock.
In the same manner, the invention can also be used in optionally replaceable tooth brush heads in powered (electrical) tooth brushes in that the bristle stock of such a replaceable tooth brush head is provided with the inventive bristles, optionally, in defined regions only. In particular, a rotary drive produces a particularly good effect in narrow gaps, fissures or the like. Spreading of split bristles is thereby supported by the centrifugal action.
If the bristle stock also comprises other, conventional bristles in addition to the inventive bristles, the latter preferably project past the former to be effective when first applying the brush. The applicant""s method according to EP 0 346 646 A1 is recommended for bringing the ends of all bristles of a bristle stock to different levels.